The relation of nonequilibrium thermodynamics to some failure and fracture theories of rock mechanics is investigated. The basic concepts are given to connect failure to the properties of material equations describing the elastic properties. The resulted in thermodynamic conditions are proved to be compatible with classical localization and failure theories of solid materials. Compatibility with experiments and some empirical, adhoc failure criteria of rocks is also demonstrated
In continuum physical theories the complex mechanical properties of material are described by constitutive functions. One of the basic construction methods to get reasonable constitutive functions is based on the Second Law of thermodynamics. The material equations have to be compatible with the Second Law in every system where dissipation occurs,. including fracture and failure of rock materials, too. Here (of course) thermodynamics is understood not only as a theory to deal with thermal phenomena and temperature changes, but as the theory dealing with the stability of materials. In this respect Second Law is understood as a requirement of stability, restricting the possible material equations of all media. In rock mechanics the pure mechanical properties are modeled by continuum mechanical methods, and even the violations of material stability are understood in most cases as pure mechanical phenomena using fracture mechanics as modeling tool. Fracture mechanics deals with holes (cracks) and discontinuities embedded in an ideal mechanical continuum. Several works use statistical methods to understand the interaction and interlocking of cracks in the mechanical continuum. In rocks damage processes include not only microcracking and interlocking of cracks but several other different mechanisms, therefore the applicability of this kind of statistical considerations is questionable.
